Method of preparing photographic materials



Jan. 16, 1962 F. D. MILLER ETAL 3,017,239

METHOD OF PREPARING PHOTOGRAPHIC MATERIALS Filed Jan. 26, 1959 2 Sheets-Sheet 1 FRANK D. MILLER CHARLES R. ADLER 1N ENTORS BY %MW ALA-XZK LW Jan. 16, 1962 F. D. MILLER ETAL METHOD OF PREPARING PHOTOGRAPHIC MATERIALS Filed Jan. 26, 1959 2 Sheets-Sheet 2 Hg 2 /2'\. EE LE E co/mE/vsEfi p p STE-AM PRESSURE /4 //vLEr IND/CA TOR 5/5070}? 52%? n AsH WA T5,?

STEAM //V/ ET :1;1: 200mg 1 PRESSURE LEVEL 654/? A PUMP /6 SENS/N6 0EV/cE VALVE 70 60/] m0 HOPPER L F lg. 3 WASH PUMP PUMP T0 LOW 555f PRESSURE SIDE OF TRANSMITTER AND TOP OF THE r0 HIGH PRESSURE EVAPORA 70/? (47' SIDE OF TRANSMITTER 7OPERATI/VGJ/VACUUM} F lg. 4 k E I I NEEDLE b v 3 VALVE DIAPHRAGM /v0zzLE STEAM FEED l STEAM STEAM 0 TROLL R INLET c N E ATMOSPHERIC STEAM BLEED THROUGH ourLEr OR/F/CE PRESSURE LEVEL SE/VS/IVG DEV/CE figgfl? TRANSMITTER VALVE A r0 00A T/IVG HOPPER FRANK 0. MILLER PUMP cHARLEs R. AOL/5R INVENTORS L A TTORNEYS M11289 Patented Jan. 16, 1962- This invention relates to a process of preparing photo graphic film and paper which involves passing a gelatin silver halide photographic emulsion preliminarily through a vertical agitated falling film type evaporator and immediately coating out the concentrated photographic emulsion thus obtained onto a support therefor usingan extrusion coating procedure. I h

In the usual procedures for preparing photographic products acoating of a photographic emulsion having a considerable content of water is app-lied to the support.

The emulsion layer resulting is ordinarily subjected to a setting effect immediately at coating, such as by chilling or by ammonia fuming as taught in US. Patent No. 2,652,345 of J. E. Jones. The latter procedure depends upon the presence of formaldehyde or some material having similar properties in the photographic emulsion. After setting, the emulsion coating is dried by conditioned air which removes a considerable amount of water therefrom to obtain the final product.

One object .of our invention is to provide a method of preparing photographic products in which the emulsion layer immediately solidifies upon application to the support therefor which makes for high speed operations. Another object of our invention is to provide a method for concentrating gelatin-silver halide emulsions which will not alter the photographic properties of the emulsion in the concentrating operation. A further object of our invent-ion is to provide a procedure for concentrating photographic emulsions regulated by controls which are motivated by a device which senses the liquid level in the outlet of the concentrating apparatus. A further object of our invention is to provide a procedure for preparing emulsion coated products wherein the setting of the emulsion upon its application to the support therefor is simplified, eliminating the necessity of setting sections which have been provided in previous coating operaions. A still further object of our invention is to assure uniformity in the application of an emulsion layer to a support in making photographic films and papers. Other obiects of'our invention will appear herein.

We have found that photographic products may be obtained without many of the difii'culties involved in previous procedures for their manufacture by the combination of an extrusion coating operation and a com patible procedure in which the gelatin emulsion is passed through a thin film evaporator by which a considerable proportion of the water therein is removed from the emulsion which is obtained in' a heated fluid condition. This heated concentrated emulsion is passed to the hop per of the coating apparatus from which aribbon of the coating composition is applied to the support. I The coating operation is of the extrusion type as described in US. Patent No. 2,681,294 of Albert E. Beguin,which in operating in accordance with our invention can be used with or without differential pressure, B y adapting this coating method to the preliminary treatment of theemulsion herein described coating speeds are 4 greatly enhanced and immediate setting of the coating when deposited upon the support occurs as a result of decrease of the emulsion temperature.

Our invention can be better understood by describing the apparatus in which the emulsion is treatedin preparation for the coating operation.

Referring particularly to FIGURES 1 and 2, FIGURE 1- shows partly in section and partly in elevation the thin film evaporator into which the photographic emulsion is introduced. Ordinarily, photographic emulsions have a" solids content of 5l5% of solids. The emulsion 1s introduced through pipe 14 into the middle portion of the device shown in FIGURE 1. The lower portion of the device indicated generally at to is the evaporator portion of the apparatus and the upper portion indicated generally at 12 is the separator portion thereof. The liquid to be concentrated is introduced through a pipe or fitting 14 which is generally located between the evaporator 16 and the separator 12. The liquid introduced at this point flows down the evaporator ltlby gravity. The concentrated liquid is drained off by a pipe 16 at the bottom "of the evaporator 10 and the water vapor formed is discharged through a pipe or conduit 18 in the upper portion of the separator 12. The evaporator part has a wall 20 which is normally cylindrical throughout its entire length. This wall is ordinarily truly cylindrical when applied to the evaporator would,,,include also a tapered form of wall. The wall 20 isheated bymeans of a steam jacket with which the evaporator portionis supplied, which steam jacket has a steam inlet 2 and outlet 3. V H a The separating chamber 12 maybe a continuation of the evaporating chamber is or preferably is larger diameter than that chamber. It is provided with fins 15 held in place by reinforcing rings 26. A cap 34 is removably secured to the top of the separator portion 12, which cap carries a bearing housing and bearing 42 at its upper end to hold shaft 46 which is rotatably mounted therein. The housing and bearing are provided with oil sea-ls at their upper and lower ends to prevent leakage of oil along the shaft in the Well known manner. The apparatus is constructed to retain the diiferential in pressure between the outside and the inside of the chamber of the concentrating apparatus. 7 a

The apparatus is provided with a rotor, fitted with blades or vanes 47, which vanes extend continuous longitudinally in the lower portion and are in close ing housing driven by a suitable source of power such as an electrical motor 51. In use, the rotor is rotated but the exact speed of rotation is not critical. Successful operation hasbeen carried on with a circumferential rotor speed of 3050 ft. per second; A description of apparatus of this type is found in US. Patent No. 2,596,- 0 86 of Muller, I I a A Although the concentrator has been shown in a vertical position, it may instead be positioned in an inclined or horizontal position particularly if so arranged that the film of emulsionis caused by gravity to pass from the inletto the outlet of the concentrating apparatus. Modification in the location of the level control may be made to accommodate such a change in position. I

FIGURE 2 is a flow sheet illustrating the arrangement of the evaporating system. Marked are the separator portion 12 and the evaporating portion 10 of theevapora tor. Vapor outlet conduit 18 is connected through a vacuum control valve to a condenser and a source of vacuum '(here a steam ejector). Pipe or fitting 14 through which the emulsion is introduced to the evaporator is connected through a valve to a gear pump which pumps the emulsion at a uniform rate into the apparatus. The concentrated emulsion is withdrawn through pipe 16 which is fitted with a pressure level sensing device shown in more detail in FIGURE 3. This instrument is connected to a differential pressure transmitter which regulates the steam supply to the jacket of the evaporator so as to control the operation. That the emulsion is not being sufiiciently concentrated would be shown by a rise in the level of the liquid in the outlet 16. This is determined automatically by the sensing device which in that case would increase the amount of steam supplied to the apparatus. If, on the other hand, the emulsion is being concentrated to too great an extent a fall in level is detected and the amount of steam introduced is automatically decreased.

In the operation of the arrangement illustrated in FIG- URE 2, both the gear pump supplying the emulsion feed to the evaporator and the gear pump withdrawing the concentrated emulsion from the evaporator are run at constant rates which rates are maintained in constant ratio, one to the other. The ratio of the rates at which these gear pumps operate is governed by the concentration of emulsion which has been selected for the evaporator to deliver and the pump rates are set to correspond to that concentration. This rate is arrived at by the actual operation of the evaporating system, but once the rate has been determined the pump is run at that constant rate throughout the operation as is also the pump supplying the emulsion feed to the evaporator.

The emulsion supply gear pump is set at a rate to supply the correct quantity of solids for the coating width and speed to be used. The gear pump withdrawing the concentrated emulsion is set at a rate so that the degree of concentration so obtained gives the desired coating properties in the fluid. This concentration is arrived at by coating experience; the withdrawing gear pump rate can then be calculated from the knowledge of feed concentration and pumping rate and desired concentration for coating.

FIGURE 3 is a sectional view of the pressure level sensing device which is attached to the outlet of the evaporator. Any change in the level of the liquid in the outlet tube changes the position of the diaphragm of the sensing device, notice of which is sent to the differential pressure transmitter to which this sensory device is attached. One tube of the sensing device is attached to the high pressure side of the differential pressure transmitter and the outlet tube to the low pressure side of the transmitter and to the top of the evaporator whereby it is under the vacuum at which the evaporator is operated. The position of the diaphragm determines the amount of flow through the nozzle of the sensing device which activates the differential pressure transmitter. The differential pressure transmitter is a well known measuring instrument, marketed by various instrument companies such as Taylor Instrument Company of Rochester, New York. Since in the sensing device the output pressure change is only on the order of a fraction of an inch of water. it is desirable for control purposes to convert this narrow absolute range to a gauge range of 3-15 p.s.i. Therefore. the sensory output and the evaporator vacuum are connected to the pressure differential transmitter which is adjusted to give the 3-15 p.s.i. output for the liquid level range desired.

FIGURE 4 is a block diaphragm showing the control system by which the intake of steam is regulated. The differential pressure transmitter activates a steam controller which varies the introduction of steam to the jacket surrounding the lower part of the evaporator. When the level of liquid in the outlet tube lowers, the emulsion is being concentrated to too great an extent which calls for a decrease in the flow of steam. Upon lowering of the liquid level the diaphragm of the liquid level sensor recedes from the nozzle opening and a greater flow of air occurs. If, on the other hand, the liquid level rises, the concentration of emulsion is not proceeding to the extent desired. The rise of liquid level is shown by decrease in the flow of air through the sensor which decrease is picked up by the pressure difierential transmitter. The steam controller causes an increase in the flow of steam to the steam jacket governed by the rise of the liquid level in the outlet tube. The emulsion is concentrated in the evaporator to a composition containing 30-60% solids which concentrated emulsion is withdrawn from the concentrator by means of a gear pump and that concentrated emulsion is transmitted through a jacketed tube (not shown) to the hopper of an extrusion type coating apparatus.

The temperature of the concentrated emulsion as it is transmitted to the coating apparatus may be kept at or near that at which it comes from the concentrator or it may be allowed to lose some heat providing that the temperature is maintained above the setting or string-forming temperature range of the concentrated emulsion. This setting or string-forming temperature may be 20 or more degrees below the temperature of the emulsion as it comes from the concentrator. In practice, it is ordinarily de sirable that the temperature of the emulsion drop some prior to coating as it is usually an advantage if the coating can be made with the emulsion at a higher viscosity than that which the emulsion should have for best operation of the concentrator. It is a feature of our invention that the concentrated emulsion is not allowed to drop in temperature as much as 20 F. below its temperature when it emerges from the concentrator.

In operation. the emulsion is fed at a controlled rate into the feed inlet 14 of the evaporator. This emulsion is uniformly distributed by the rotation of the rotor upon the inner wall of the evaporator and flows by gravity to the bottom thereof. The emulsion is subjected in the evaporator to heat and vacuum and the water vapor and noncondensible gases are drawn out through the vapor outlet. The foam which forms when emulsions are subjected to this treatment is mechanically broken in the separation section and falls back as a liquid. The rotor thus serves both as a foam breaker and a means of mechanically agitating the firn in the heating section to promote heat transfer. In the concentrating of photographic emulsions in accordance with our invention it has been found that the use of vacuum within the range of 20-28 inches of mercury and steam temperatures of -265 F. are satisfactory. It has been found that photographic emulsions can be concentrated such as from 10% solids to 50% solids in a very short time such as 30 seconds or less by this method without any overlapping occurring. If the photographic emulsion to be applied to a support has unusual hardening characteristics so that difficulties would be encountered in concentrating it, it is desirable in that case to withhold the hardening agent from the emulsion while being concentrated, and introduce the hardener into the emulsion just before coating or as a layer upon the emulsion coat at the time of coating.

The emulsion after concentration and while still warm is led to the hopper of an apparatus shown in FIGURE 1 of US. Patent No. 2,681,294, and from there through the slot directly to the film base or paper base which is coated by the procedure employed there, with or without the difierential. pressure. The concentrated emulsion which isat an elevated temperature is cooled by contact with the support and because of the lowered water content thereof solidifies immediately upon coating. The photographic material thus obtained needs only treatment for a short time with conditioned air to remove the remaining moisture from the emulsion layer. It is understood that the entire operation in accordance with our invention is carried out under darkened conditions to retain the photosensitive characteristics.

The following examples illustrate the preparation of photographic products in accordance with our invention.

Example 1 A coating 4 inches wide of a concentrated gelatin silver halide emusion is to be made at 100 ft. per minute to give a coverage of 0.415 lb. of dry solids per 100 sq. ft. This is equal to a rate of 0.138 lb. of dry solids per minute. A gelatin silver halide photographic emulsion having a solids content of 12% was pumped by means of a positive dis-' placement gear pump with a variable speed drive at the exact rate of 1.15 lbs. per minute to an agitated film evaporator, as described herein, having 1 sq. ft. of heating surface. This rate of feed of the dilute solution carries the exact amount of solids to supply the required coverage of 0.415 lb. per 100 sq. ft. Steam is supplied to'the evaporator at a temperature of 249 R, which temperature is controlled by regulation of the steam pressure. The pressure in the evaporator is reduced to approximately 1.94 lbs. per sq. inch absolute pressure, which corresponds to a vapor temperature of 125 F., by means of an ejector or other suitable vacuum source.

The rotor blades in the evaporator were operated at a linear speed of 2090 ft. per minute with a clearance between the ends of the blades and the heating surface of & inch which operation spread the emulsion on the heating surface of the evaporator in the form of a thin agitated film, Because the temperature of the heating surface is well above the equilibrium vapor temperature, the emulsion boils as it falls by gravity down the walls of the evaporator. The water so vaporized is carried out of the evaporator through a suitable condenser and subsequently removed, together with any non-condensible gases by means of the ejector or other vacuum source. The emulsion flowing down the walls becomes more concentrated until it leaves the heating surface and collects in the discharge line of the evaporator at the bottom. At the end of the discharge line the emulsion flows through a multiport valve to an accurately controlled positive displacement gear pump known as the product pump. The multiport valve is also connected to a wash pump for cleaning purposes. The product pump speed is set to discharge at the exact rate at which the product is con centrated. The temperature and pressure were selected to produce a concentration of 39% solids in the product and therefor the product pump rate was 0.354 lb. per' minute. To insure maintaining the 39% concentration the level of the concentrate in the discharge pipe from the evaporator was accurately sensed by a pressure level sensing device which controls the temperature of the steam 1n the evaporator jacket. Thus, if a deposit accumulates on the evaporator walls and therefore reduces the product concentration, the level tends to rise in the discharge pipe since both feed and product pumps operate at constant volume. This is sensed by the level control which in turn raises the steam temperature, thereby maintaining the desired concentration. In the beginning of the operation the level sensing device may be so connected as to regulate the product pump speed. The concentrated emulsion was pumped directly from the product pump through a water jacketed tube to an extrusion hopper maintained on a coating machine ofthe type shown in FIGURE 1 of U.S. Patent No. 2,681,294. The emulsion coating was applied to paper base to immediately form an emulsion layer thereon which set upon contact with the paper without any penetration into the fibers thereof. The moisture was removed from the emulsion layer by the use of a current of warm dry air in the conventional manner. Photographic paper was obtained having a smooth coating of the desired weight on the paper.

Example 2 A coating of a gelatin-silver halide photographic emulsion 36 inches wide was desired at the rate of 80 ft. per minute and with a dry solids content of .339 lb. per 100 6 sq. ft. A gelatin-silver halide photographic emulsion having a solids content of 9.50% was used. The emulsion was pumped from a holding kettle to the evaporator by means of two gear pumps operating in parallel from a common variable speed drive, two pumps being used instead of one to permit operating at low speeds and therefore reduce wear and maintain accuracy. The pumps were driven at such a speed as to accurately deliver 4.28 lbs. per minute each or a total of 8.56 lbs. per minute of emulsion containing .813 lb. per minute of dry solids. The evaporator to which the pumps direct the emulsion was of the agitated film type having 18 sq. ft. of heating surface with a bladed rotor turning at a peripheral speed of 2090 ft. per minute. The steam jacket of the evaporator was divided into 2 parts and the upper and lower halves of the jacket were maintained at different temperatures. The upper jacket was supplied with steam at 194 F. and lower jacket was supplied with steam at 260 F., the steam being obtained from the higher pressure source through reducing valves to the two separate steam jackets. The emulsion entered the top of the heat transfer section of the evaporator and was spread in a thin film on the inner wall of the evaporator section by the action of the rotor blades. The pressure in the evaporator is maintained at approximately 1.94 lbs. per square inch absolute pressure, which corresponds with a vapor temperature of 125 F., this reduced pressure being maintained by means of a steam ejector. The emulsion upon the walls of the evaporator gave up water vapor as it flowed down the wall to be collected in the discharge pipe. The water vapor obtained was carried out of the evaporator through a suitable condenser and was removed together with any non-condensible gases by the ejector.

The discharge pipe of the evaporator was connected to a suitable pump and the concentrated emulsion was removed from the evaporator to the inlet of a variable speed driven gear pump, known as the product metering pump. The constant pressure at the inlet of the product metering pump is obtained by providing a discharge pump with considerably higher capacity and' a'rranging about it a recirculating line, the volume recirculating being controlled by a pressure sensing device at the inlet of the metering pump which controls the regulating valve in' the recirculating line. The speed of the metering pump was set to deliver exactly 2.70 lbs. per minute of concentrated emulsion which is the quantity of a 30.5% solution containing .813 lb. per minute of dry solids. This concentration was selectedon' the basis of previous experience having shown that it would have the required coating properties. The concentrated emulsion was forced through a water jacketed tube through an extrusion type hopper mounted on a coating machine. The coating operation was carried out as described in U.S. Patent No. 2,681,294, cellulose triacetate film base being coated in this operation.

The following table gives the range of conditions used in' concentrating 1 type or" gelatin-silver halide photographic emulsion in accordance with our invention.

Feed concentration 12% solids. Cone. used:

(1) Percent solids 18-45%.

(2) Visc., cp., at F. 200-5000. Evaporator pressure, p.s.i.a. 1.4-2.0. Vapor temperature, F. -125. Steam temperature, F. 2 jackets180-270. Product density, gm./ml 1.12-1.28. Conc. ratio (usual) 3.25-3.50.

In another case a different type of photosensitive silver halide emulsion was concentrated in an agitated film evaporator. The solids concentration in this type emulsion was greater than that previously concentrated. The conditions used there were as follows:

Feed concentration 15.3% solids. Conc. used:

(1) Percent solids 55-60%.

(2) Visc., cp., at 105 F. 2500-5000. Evaporator pressure, p.s.-i.a. 1.4-2.0. Vapor temperature, F 110-125. Steam temperature, F 2 jackets-180-270. Product density, gm./ml 1.49-1.53. Conc. ratio (usual) 3.75-4.00.

The useful range of pressures in concentrating the emulsion within the evaporator are found within the range of I ls-5 lbs. per sq. inch absolute and the useful steam temperatures are found Within the range of 150 F.-280 F. The feed solutions may vary from as little as 2 or 3% solids up to as high as 25% solids and the emulsion concentrations may range anywhere from 25-65% solids or higher depending on the composition of the material and how highly concentrated they must be in order to obtain good coatability.

In some cases it may be desirable to pass the emulsion a second time through the concentrating apparatus to obtain the desired concentration. For instance, in the case of some feed solutions which contain 8% or less of solids and a concentration of 50-60% solids in the emulsion is desirable to obtain good coatability, it might be necessary to run the emulsion through twice. For continuous operation this is most conveniently accomplished by using 2 evaporators in series or a single evaporator which recycles a large proportion of discharge back to the evaporator.

The concentrated emulsion as it comes from the evaporator will have a temperature within the range of 85-130 F. and the emulsion is maintained at that temperature in transferring it from the evaporator through a jacketed tube maintained at 85-130 F. to the hopper of the extrusion coating device. The concentrated emulsion has a viscosity of at least 1000 cps. (usually 2000-5000 cps.) at this temperature. When the emulsion having this temperature and viscosity is applied to the support in the extrusion coating operation the emulsion layer formed sets apparently due to the lowering of the temperature upon exposure to the support and to the air and to the concentration of the emulsion. The emulsion ceases to be flowable at room temperature and at temperatures within the range of 85-130 F. the concentrated emulsion is of such viscosity that only a pressure considerably above that contributed by gravity causes flow of the emulsion.

We claim as our invention:

1. A process of preparing photographic products which comprises passing a gelatin-silver halide photographic emulsion having a solids content within the range of 5- through an agitated falling-film type evaporator whereby an emulsion is obtained having a solids content within the range of 30-60% and a temperature within the range of 85-130 F., transferring the concentrated emulsion to the hopper of an extrusion coating device while substantially maintaining its temperature and extruding the emulsion as a layer upon a support for the emulsion,

all under darkened conditions, whereby a photosensitive photographic product is obtained.

2. A'process for preparing photographic paper which comprises passing a gelatin-silver halide photographic emulsion having a solids content of approximately 12% through an agitated falling-film type evaporator whereby an emulsion is obtained having 39% solids content and a temperature of 130 F., transferring the concentrated emulsion to the hopper of an extrusion coating apparatus while substantially maintaining its temperature and extruding the emulsion as a layer upon a paper base, all under darkened conditions, whereby a photosensitive photographic paper is obtained.

3. A process for preparing photographic film which comprises passing a gelatin-silver halide photographic emulsion having a solids content of approximately 9.50% through an agitated falling-film type evaporator whereby an emulsion is obtained having 25-65% solids and a temperature within the range of 85-l30 F., transferring the concentrated emulsion to the hopper of an extrusiontype coating apparatus while substantially maintaining its temperature and extruding it onto film base, all under darkened conditions, whereby a photosensitive film base is obtained.

4. A process of preparing photographic products which comprises passing a gelatin-silver halide photographic emulsion of 5-15% solids content through a vertical agitated falling-film type evaporator whereby water is driven off and an emulsion is obtained having a solids content of 30-60% and a temperature within the range of 85-130 F., transferring the concentrated emulsion to the hopper of an extrusion coating device while maintaining its temperature above that at which solidification occurs from which device the emulsion is extruded upon a support for the emulsion, all under darkened conditions, whereby a photosensitive photographic product is obtained.

5. A process of preparing photographic products which comprises subjecting a gelatin-silver halide photographic emulsion having a solids content within the range of 5-15%, while in the form of an agitated film to an elevated temperature whereby an emulsion having a solids content within the range of 30-60% and a temperature within the range of 85130 F. is obtained, transferring the concentrated emulsion while substantially maintaining its temperature to the hopper of an extrusion coating apparatus and extruding the emulsion as a layer upon a support therefor, all under darkened conditions whereby a photosensitive photographic product is obtained.

References Cited in the file of this patent UNITED STATES PATENTS 2,121,205 Lippert et a1. June 21, 1938 2,168,051 Smith et a1. Aug. 1, 1939 2,596,086 Muller May 6, 1952 2,681,294 Beguin June 15, 1954 2,812,019 Rasmussen Nov. 5, 1957 2,844,607 Gushin et al. July 22, 1958 2,857,962 Rogers Oct. 28, 1958 

1. A PROCESS OF PREPARING PHOTOGRAPHIC PRODUCTS WHICH COMPRISES PASSING A GELATIN-SILVER HALIDE PHOTOGRAPHIC EMULSION HAVING A SOLIDS CONTENT WITHIN THE RANGE OF 515% THROUGH AN AGITATED FALLING-FILM TYPE EVAPORATOR WHEREBY AN EMULSION IS OBTAINED HAVING A SOLIDS CONTENT WITHIN THE RANGE OF 30-60% AND A TEMPERATURE WITHIN THE RANGE OF 85-130*F., TRANSFERRING THE CONCENTRATED EMULSION TO THE HOPPER OF AN EXTRUSION COATING DEVICE WHILE SUBSTANTIALLY MAINTAINING ITS TEMPERATURE AND EXTRUDING THE EMULSION AS A LAYER UPON A SUPPORT FORTHE EMULSION, ALL UNDER DARKENED CONDITIONS, WHEREBY A PHOTOSENSITIVE PHOTOGRAPHIC PRODUCT IS OBTAINED. 